In recent years, organic thin-film light emitting devices have been actively studied, which emit light when electrons injected from a cathode and holes injected from an anode are recombined in an organic luminous body placed between the electrodes. Such light emitting devices are attracting attention, because they are thin and characterized by high-luminance light emission at low driving voltage and multicolor light emission from selected emissive materials.
Since C. W. Tang et al. of the Eastman Kodak Company reported an organic thin-film light emitting device capable of emitting light with high luminance, many research institutes have conducted the research. The typical structure of the organic thin-film light emitting device proposed by the research group of the Eastman Kodak Company includes an ITO glass substrate, and a hole transporting diamine compound, an emissive layer of tris(8-quinolinolato)aluminum(III), and a cathode of Mg:Ag (alloy) sequentially provided on the substrate, which was capable of emitting 1,000 cd/m2 of green light at a driving voltage of about 10 V (see Applied Physics Letters (U.S.), 1987, Vol. 51, No. 12, pp. 913-915.).
Organic thin-film light emitting devices have also been actively studied for display applications and so on, because they can emit light of different colors, when different fluorescent materials are used in the emissive layer. Among emissive materials of three primary colors, the research of green emissive materials is most advanced. Now, active researches have been conducted to improve the properties of red and blue emissive materials.
One of the most important objects in organic thin-film light emitting devices is to allow the devices to have satisfactory luminance efficiency and durability at the same time. Particularly for blue light emitting devices, few blue emissive materials can form a device with a high level of durability and reliability. For example, there are disclosed blue light emitting devices using aryl-substituted pyrene compounds (see Japanese Patent Application Laid-Open (JP-A) No. 2000-273056 (claims 1 and 2), JP-A No. 2002-63988 (claim 1), JP-A No. 2004-75567 (claims 1 to 4) and JP-A No. 2004-139957 (claim 1)). There is also disclosed a blue light emitting device using a pyrene compound having four dibenzofuranyl groups (see PCT pamphlet of International Publication No. 2004/096945 (claims)). However, these devices all have insufficient durability.